In order to display his own messaged he looked into how the HFP is implemented in the Bluetooth stack. The details are shared in his readme file but it goes something like this: The Bluez package needs to be compiled with a dummy backend that is not phone-specific and that will then allow external manipulation of the data being sent. This provides something of an API that a Python script can manipulate. His proof-of-concept allows for the script to be called with the message you want displayed as the command line argument. This should be simple enough to incorporate for just about any purpose that suits your fancy. Unfortunately, messing with the Bluetooth package in this way makes it impossible to use other devices with your phone, but that’s a hack for another day.